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Oceanography > Surface and deep ocean circulation through time- LGM > Flashcards

Surface and deep ocean circulation through time- LGM Flashcards

1
Q

Evidence for ice activity-indicating ice movement

A
  • Erratic boulders
  • Striae
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2
Q

What controls long-term climate chage?

A

Variation in Earth’s orbital parameters- Milankovitvh theory

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3
Q

Eccentricity

A

Variation of the Earth’s path around the sun- 100ka and 400ka

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4
Q

Obliquity

A

Variation of Earth’s rotational axis with respect to its rotational plane around the sun- 41ka

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5
Q

Precession

A

Wobble of the rotational axis - 19-24 ka

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6
Q

1-6% eccentricity (circular to elliptical)

A

Takes 100,000 years

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7
Q

Aphelion

A

Distant path position to the sun

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8
Q

Perihelion

A

Close path position to the sun

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9
Q

Earth’s axial tilt varies from 24.5 to 22.1 degrees

A

Every 41,000 years

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10
Q

What impact does axial tilt (obliquity) have?

A

Effects the distribution of solar radiation on Earth’s surface- when tilt decreases, polar regions receive less sunlight

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11
Q

Impact of changing precession?

A

Alters which hemisphere receives more sunlight during the summer

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12
Q

Evidence for the Milankovitch cycles?

A

Assemblages of particles (biogenic or lithogenic) within the ocean- sedimentation

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13
Q

Most frequently used ‘tool’ used to reconstruct ocean circulation patterns

A

Planktonic and benthic foraminifera

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14
Q

Oxygen isotopes incorporated in foraminifera that reflect T an S of sea water

A

18O and 16O incorporated as part of the CaCO3 test

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15
Q

Two carbon isotopes incorporated into the test of foraminifera

A

13C and 12C

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16
Q

The older the water mass…

A

The higher the 12C concentration in the water and the foraminifera tests

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17
Q

Which C isotope end up in organic tissue in a higher amount?

A

12C

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18
Q

When organisms die…

A

Organic matter sinks to the floor taking 12C rich tissue with it- extracting 12C from the surface ocean and oxidizing organic matter on its way down the water column and releasing 12C back into the ocean at depth= BIOLOGICAL PUMPING

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19
Q

NADW- isotope values

A

NADW starts with high carbon isotope values- on its way towards the Pacific–> addition of 12C by oxidizing organic matter DECREASES CARBON ISOTOPE VALUES

20
Q

Carbon isotope signature of AABW

A

Very low carbon isotope values

21
Q

Oxygen isotope- evaporation

A

During evaporation 18O and 16O enter the vapor phase at a different rate. 16O more enriched in water vapor that 18O

22
Q

16O evaporation

A

Evaporates much quicker than 18O

23
Q

Oxygen isotopes in foraminifera are controlled by 3 parameters:

A
  1. Temperature
  2. Variation in size of continental ice masses
  3. oxygen isotopes of the ambient seawater (out of which the foraminifera calcifies its test)
24
Q

Difference in oxygen isotope values between surface and deep ocean:

A

Reflect the temperature gradient between surface and deep ocean

25
Q

Change in oxygen values in foraminiera with temp?

A

Warmer temps= favour 16O incorporated into CaCO3 test
Colder temps= favour 18O

26
Q

Consequences of waxing and waning of continental ice masses for the ocean:

A
  1. A lot of 16O extracted from ocean and stored in the ice leading to higher oxygen isotopes in water
  2. Extracted water led to lowered sea level
27
Q

Piston Corer

A

Can retrieve sediment cores from the soft seabed to depths of 30m. The piston prevents water from entering the core barrel- preserving sediment layers

28
Q

Gravity Corer

A

Retrieves sediment cores from soft- medium firm sediments from a few m to tens of m. Lowered and collected sample by its weight - cheaper than piston corer but shorter samples

29
Q

Box corer

A

Can collect LARGE UNDISTURBED sediment samples however only on the top layer of sea floor. Collection by weighted box and two hinged spade doors

30
Q

Multi corer

A

Multi corer for short sediment sequences. Provides excellent surfaces sediment/bottom water samples. Better than box corer, but more fragile, entailing risk of destruction. Length of sediment section depends on design (50-60cm max)

31
Q

Steps leading from LGM–> Holocene

A
  1. Deglacial step- terminated LGM
  2. B-A Oscillation
  3. Younger Dryas (YD)
32
Q

B-A Oscillation

A

Bolling-Allerod Oscillation; two short warm pulses separated by a short cold event

33
Q

IRDs during the glaciation

A

Ice rafted debris (IRD) - icebergs drifted off to Portugal leaving a trail of IRD- implies meltwater being around at the sea surface

34
Q

Sediment transport associated with Heinrich events

A

IRD released from icebergs and suspended sediment in meltwater

35
Q

Surface ocean conditions-LGM

A

Much colder N.Atlantic with a few icebergs around an expanded sea ice cover
–> Gulf Stream= weakened (most of the flow re-routed eastward)

36
Q

Meltwater world (Heinrich Event 1)

A

Cold in general, additional cooling in some locations, flotillas of icebergs around accompanied by meltwater

37
Q

The Holocene

A

Modern warm period

38
Q

Planktonic foraminifera

A

Reflect surface ocean conditions

39
Q

Benthic foraminifera

A

Reflect bottom ocean conditions

40
Q

Projection plane

A

Individual locations projected onto the projection plane according to location and water depth

41
Q

Sediment dating

A

Used to establish the rate a particular section has been deposited

42
Q

Time slice approach

A

Defining sediment sections that contain info from a specific time period

43
Q

NADW- LGM

A

The likely sources areas for glacial NADW shifted to an area south of Iceland

44
Q

Meltwater period (Heinrich Event 1) - NADW

A

Meltwater from ice caps melting reaches source areas of NADW reducing salinity- NADW formation REDUCES.

45
Q

Changes in T/S properties in the N-Atlantic

A

Large volume of ice= water volume reduced and salinity increased (1psu) - affects convention in areas of Deepwater formation

46
Q

Younger Dryas (YD)

A

Return to glacial conditions in less than 100 years
–> Maybe caused by a reduction in North Atlantic Conveyer Belt

Oceanography (23 decks)

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